1. Field of the Invention
The present invention relates to an organic/inorganic laminate, more precisely, to an organic/inorganic laminate having a specific organic layer and therefore having a lowered water vapor permeability. Further, the invention relates to a barrier film substrate comprising the laminate, and to a device and an optical member comprising the barrier film substrate.
2. Description of the Related Art
Heretofore, a barrier film fabricated by forming a thin metal oxide film of aluminium oxide, magnesium oxide or silicon oxide on the surface of a plastic film is widely used for wrapping or packaging articles that require shielding from various gases such as water vapor or oxygen and for wrapping or packaging edibles, industrial articles and medicines for preventing them from being deteriorated.
Recently, in the field of liquid-crystal display devices and organic EL devices (organic electroluminescent devices), plastic film substrates are being used in place of glass substrates that are heavy and readily cracked or broken. As applicable to a roll-to-roll system, plastic film substrates are advantageous in point of cost. However, plastic film substrates are problematic in that their gas-barrier property is not good as compared with that of glass substrates. Therefore, when a plastic film substrate is used in a liquid-crystal display device, then water vapor may penetrate into the liquid-crystal cell, thereby causing display failures.
For solving the problem, it is known to form an organic/inorganic laminate on a plastic film, thereby using the resulting barrier film substrate. JP-A 2002-264274 discloses a barrier film substrate that comprises a laminate of an organic layer formed by curing a composition containing a 6-functional acrylate or methacrylate monomer or oligomer, and an inorganic layer of an oxide selected from an aluminium oxide, a silicon oxide, an indium/tin composite oxide and an indium/cerium composite oxide. JP-A 2002-264274 says that a higher content of the 6-functional acrylate monomer or the like within a range of at most 30% by mass increases the barrier capability of the film, in which, however, even though the content is 100% by mass, the water vapor permeability of the film could be on a level of 0.08 g/m2/day.
On the other hand, substrates for use in organic EL devices require a further higher water vapor barrier level. Preferably, their water vapor permeability is less than the detection limit in a MOCON method, or that is, less than 0.005 g/m2/day. To satisfy the requirement, U.S. Pat. No. 6,413,645 discloses a technique of providing an alternate laminate of plural organic layers and inorganic layers as a barrier layer, thereby realizing a water vapor permeability of less than 0.005 g/m2/day. The patent specification says that in case where only one organic layer and one inorganic layer are laminated, then the water vapor permeability of the resulting laminate is 0.011 g/m2/day, explicitly indicating the technical advantage that results from multilayer lamination.
However, in consideration of the industrial applicability, the multilayer lamination of organic layers and inorganic layers as in U.S. Pat. No. 6,413,645 lowers the producibility, and is therefore seriously problematic in industrial mass-production of barrier film substrates. For industrially mass-producing a large number of barrier film substrates at low cost, it is desired that a smaller number of layers in multilayer lamination could exhibit higher barrier capability. From the background, it is desired to develop an inorganic/organic laminate of one pair of an organic layer and an inorganic layer and capable of attaining a water vapor permeability of at most 0.005 g/m2/day, especially less than 0.001 g/m2/day, to develop a barrier film substrate comprising the laminate, and to develop an organic EL device comprising the barrier film substrate.